Arkansas Concrete - Residential Exam

Topic: Estimating All content below is drawn from Pipe and Excavation Contracting.

Key Concepts

Soil states and conversions (Pages 60–61). Soil and fill are measured in cubic yards in three states: bank cubic yards (BCY) — soil in its natural, undisturbed condition; loose cubic yards (LCY) — soil that has been excavated or disturbed and has swelled; and compacted cubic yards (CCY) — soil that has been compacted and has shrunk. Hauling unit capacities are measured in loose cubic yards. In the text's worked example, 1,000 BCY of dry common earth × 1.32 = 1,320 LCY; at a truck capacity of 14 LCY that is 95 haul trips; that 1,320 LCY placed at 100 percent Standard Proctor becomes 857 CCY (1,320 ÷ 1.54).

Import and export (Page 61). Export (spoil) is excess excavated material removed from the site; import (borrow) is acceptable material hauled onto the site. Export or import quantity is the difference between total cut and fill volumes — subtract total fill from total excavation volume. If total fill exceeds excavation volume, the project requires import; if fill is less, the project requires export.

Key Concepts

Reading plans - A plan view is a bird's-eye overhead view of the work area showing the layout of the work. A profile view is a horizontal cut-away (cross-section) view along the alignment, revealing elevations, grades and depths. (Pipe and Excavation Contracting, Page 105, Chapter 3 introduction)

Footing depth, location and anchorage - Exterior footings shall be placed not less than 12 inches below the undisturbed ground surface. Additional depth may be required for frost protection. (IRC Section R403.1.4) - Frost-protected shallow foundations: where the monthly mean temperature of the building is maintained not less than 64°F (18°C), footings are not required to extend below the frost line where protected by insulation per Figure R403.3(1) and Table R403.3(1). Shall not be used for unheated spaces such as porches, utility rooms, garages and carports. (IRC Section R403.3) - Wood sill and sole plates: minimum 1/2-inch-diameter anchor bolts spaced a maximum of 6 feet on center, extending a minimum of 7 inches into concrete or grouted cells of concrete masonry units; nut and washer tightened on each bolt; not fewer than two bolts per plate section. (2015 IRC Section R403.1.6)

Key Concepts

Cost and role of formwork. Formwork costs range from 35 to 60 percent of the cost of a concrete structure (Contractor's Guide, Page 54). Formwork is the total support system — facing material, supporting members, hardware, and bracing — and must carry its own weight, the fresh concrete, construction loads, and live loads such as snow (Page 54).

Safety and governing documents. Requirements for concrete, concrete forms, and shoring are in Subpart Q, Concrete and Masonry Construction, of OSHA 1926, "Safety and Health Regulations for Construction." Designers must follow local code and OSHA and should follow the design criteria of ACI 347R, "Guide to Formwork for Concrete," and ACI SP-4 (Chapter 5 — Safety Precautions). Self-consolidating concrete produces higher forces on forms than typical concrete, so extra care is required.

Lateral pressure. The three most important variables affecting pressure on forms are (1) concrete temperature, (2) rate of placement, and (3) weight of concrete (Page 70). Normalweight concrete weighs approximately 150 lb/ft³ (2400 kg/m³) (Page 70). Field factors that increase form pressure: lower temperatures, retarded set, higher slump, vibration, and increased lift heights (Chapter 10).

Key Concepts

Bond. The adhesion of concrete to the bar surface, plus the resistance provided by the bar deformations or ribs, keeps bars from slipping through the concrete and makes the two materials act as one. This gripping of the bars by concrete is known as bond. (Placing Reinforcing Bars, 10th ed., Ch. 3 — Concrete and Reinforced Concrete)

Bar identification. For standard American bars, the bar number indicates the nominal bar diameter in eighths of an inch — a #8 bar is 1 in. (25.4 mm) in diameter. Every deformed bar must be rolled with the producer's mill mark, size number, type-of-steel symbol, and a grade mark; no grade mark is required for Grades 40 and 50. (Contractor's Guide, Ch. 6; Placing Reinforcing Bars, Ch. 7, Fig. 7-2)

Minimum concrete cover — cast-in-place, nonprestressed (Table 6.3, Contractor's Guide p. 100; ACI 318-11 §7.7.1) - Cast against and permanently exposed to earth (such as footings): 3 in. (75 mm) - Exposed to earth or weather: #6 through #18 bars — 2 in.; #5, W31/D31 wire and smaller — 1-1/2 in. - Not exposed to weather or in contact with ground — slabs, walls, joists: #14 and #18 bars 1-1/2 in.; #11 and smaller 3/4 in. - Not exposed to weather or in contact with ground — beams and columns (primary reinforcement, ties, stirrups, spirals): 1-1/2 in. - Bundled bars: cover equals the…

(9 questions, 30% of exam)

Key Concepts

Exposure classes and w/cm limits (Contractor's Guide, Table 2.5, p. 24) - Category F3 — concrete exposed to freezing-and-thawing cycles with frequent exposure to water and deicing chemicals: maximum w/cm 0.40, minimum compressive strength 5000 psi. - Category S2 (sulfate) — dissolved sulfate between 1500 and 10,000 ppm: maximum w/cm 0.45, minimum compressive strength 4500 psi (31 MPa). - Category W1 — concrete in contact with water where low permeability is required: maximum w/cm 0.50, minimum compressive strength 4000 psi (28 MPa).

Cement types (DCCM 17th ed., Ch. 2, pp. 26, 30) - Type III – strength at an earlier period than normally expected; chemically similar to Type I but ground finer; used for early form removal and, in cold weather, a reduced curing period. - Type II(MH) – generates heat at a slower rate by limiting the heat index (C₃S + 4.75 C₃A) to a maximum of 100; for mass elements such as large foundations and thick retaining walls. - Type IV – low heat of hydration, massive structures. - Type V – severe sulfate environments; high sulfate resistance from a C₃A content of not more than 5%.

Key Concepts

Employer accident prevention responsibilities (29 CFR 1926.20, Subpart C) - "It shall be the responsibility of the employer to initiate and maintain such programs as may be necessary to comply with this part." §1926.20(b)(1) - Such programs "shall provide for frequent and regular inspections of the job sites, materials, and equipment to be made by competent persons designated by the employers." §1926.20(b)(2) - Machinery, tools, material, or equipment not in compliance is prohibited; it "shall either be identified as unsafe by tagging or locking the controls to render them inoperable or shall be physically removed from its place of operation." §1926.20(b)(3) - "The employer shall permit only those employees qualified by training or experience to operate equipment and machinery." §1926.20(b)(4) - PPE standards "impose a separate compliance duty with respect to each employee covered by the requirement… each failure to provide PPE to an employee may be considered a separate violation." §1926.20(f)(1). The same separate-duty rule applies to training. §1926.20(f)(2)